How to get a reference to the obect...

jacob · February 22nd, 2004, 02:44 PM

Well, it is probably quite simple, but I can't seem to make it work. The thing is that I would like to have a reference to the object from within the class that implements the object. I have got a class 'Users' in which I have got a method 'load'. I would like this method to initialize the object from a file, like this...

Code:

    public void load(String filename)
    {
        File f = new File(filename);
        if(f.exists())
        {
            ObjectInputStream ois = null;
            try
            {
                ois = new ObjectInputStream(new FileInputStream(filename));
                this = (Users)ois.readObject();
                ois.close();
            }
            catch(Exception e)
            {
                System.err.println("!-> error: " + e);
            }
        }
    }

In the above code I have assigned the result from readObject to 'this', which would be the intuitive way to do this, however it does not seem to work.

I have tried to make a private instance of the class and then assigning 'this' to the new instance, but then I can't use the methods of the class, which I have extended, in this...

Code:

public class Users extends Hashtable implements Serializable

It seems to be an evil circle! A work-around would be to return an object of type 'Users' from the load method and then assigning it when calling load, but I do not like this solution, since I then have to make an instance of that class and then assign it to another!

Thanks!

Jacob.

Martyn · February 23rd, 2004, 05:19 AM

jacob,

You can't just use 'this' on it's own as 'this' refers to the current object reference. You need to declare a reference of the correct type within your class and then assign the object reference to it.

FileInputStream fis = new FileInputStream("temp.tmp");
ObjectInputStream ois = new ObjectInputStream(fis);
Date date = (Date) ois.readObject();
ois.close();

Alternatively, you could load the individual fields by using the various read methods provided by the OBjectInputStream class.

Cheers

Martyn

Martyn · February 23rd, 2004, 05:49 AM

Jacob,

Having just replied I realised that I should have added the following example.

//Add this to your main
Users newUsers = (Users)load("userList");

//Replace your load method with this
public static Object load(String file)
{
   try {
      ObjectInputStream load = new ObjectInputStream(new FileInputStream(file));
      return load.readObject();
   }
   catch (Exception e) {
      System.out.println("Could not load " + file);
      return null;
   }
}

Cheers

Martyn

jacob · February 23rd, 2004, 06:21 PM

Thanks for the reply, however I think the method that you describe corresponds to the thing I meant to describe in this...

Quote:

quote:A work-around would be to return an object of type 'Users' from the load method and then assigning it when calling load, but I do not like this solution, since I then have to make an instance of that class and then assign it to another!

That is, to return an object and then assigning it when calling the method. I would like to make an instance of an object and then load, something like this...

Code:

Users usrs = new Users();
usrs.load("users.usr");
usrs.put("martyn", new User());

I am probably being fanatic

, but it should in some way be possible to do this...!?

Thanks again

Jacob.

jacob · February 23rd, 2004, 06:38 PM

Now I am suddenly not sure that we meant the same! So here is the important stuff of the 'Users' class...

Code:

public class Users extends Hashtable implements Serializable
{

    public Users()
    {

    }

    public Users load(String filename)
    {
        Users users = null;
        File f = new File(filename);
        if(f.exists())
        {
            ObjectInputStream ois = null;
            try
            {
                ois = new ObjectInputStream(new FileInputStream(filename));
                users = (Users)ois.readObject();                
                ois.close();
            }
            catch(Exception e)
            {
                System.err.println("!-> error: " + e);
            }
        }
        return users;
    }
}

...and then I have some other (very simplified) class, namely the calling class...

Code:

public class MyExampleLoadUserClassForWroxP2PForum
{
    public static void main(String[] args)
    {
        Users users = null;

        try
        {
            users = new Users();

            // Possible!
            users = users.load("users.usr");

            // Prefer something like this!
//            users.load("users.usr");

        }
        catch(Exception e)
        {
            System.out.println("!-> error: " + e);        
        }
    }
}

This works, however is not what I would like! (I am aware of the wrong error handling).

Thanks!

Jacob.